MELAS, a common mitochondrial disease associated with a m!3243A>G mutation in the tRNALeu(UUR) gene of the mitochondrial DNA, is characterized by strokes, lactic acidosis, cerebral infarction and edema. The pathogenesis of strokes and edema in MELAS is not understood. Without a proper understanding of the pathophysiology, it has not been possible to devise rational therapies for this devastating disease. Our hypothesis is that mitochondrial dysfunction in the cortical blood vessels causes a breakdown of the blood-brain barrier (BBB) leading to strokes and associated edema. We have successfully constructed a working in vitro model of a normal and MELAS BBB. We propose to study the function of the BBB in MELAS in this model. Specifically, we will analyze tight junction proteins that regulate BBB permeability, water channels, and lactate transporters and correlate our results with respiratory chain function. These in vitro studies at the cellular level will be extended to MELAS brain sections to compare and confirm our findings at the tissue level. Therapeutic management of MELAS is anecdotal and generally ineffective. Our in vitro model is a dynamic system that can be manipulated to test various BBB protective drugs, which can restore barrier function and thus can be useful therapeutic agents for strokes, lactic acidosis, and associated edema. We will use this model to test the effect of steroids in regulating water channels and of glycerphosphoinositol and interferon-b-1a in modulating the inflammatory process after strokes. First, these studies will provide insight into the physiology of the BBB. Secondly, they will reveal changes in vascular permeability in MELAS due to mitochondrial dysfunction and energy shortage. Third, the culture model will allow us to evaluate the sequence of events leading to the increase in permeability. Finally, the in vitro model provides a flexible system to test the therapeutic value of drugs to be used this devastating illness.